The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP1) with a layer of antiferromagnetic material such as PtMn. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a magnetization, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer.
The demand for ever increasing data rate and data density has led a push to develop perpendicular magnetic recording systems. Whereas more traditional longitudinal recording systems record data bits as magnetic transitions oriented longitudinally on a magnetic medium, a perpendicular recording system records data as magnetic bits oriented perpendicular to the plane of the medium. Such perpendicular recording systems require new high coercivity mediums in order to perform at their maximum potential. Perpendicular magnetic recording media include a thin high coercivity top layer formed over a low coercivity underlayer.
Suitable materials for use in the high coercivity top layer of the media are both highly corrosive and porous. In order to prevent corrosion of this high coercivity top layer, and also to allow the slider to fly over the media, a thin protective overcoat must be applied. Currently diamond like carbon (DLC) is used for this top coat, and has been considered the best material available for this purpose.
Unfortunately, higher coercivity media, and higher data rate recording systems are becoming increasingly incompatible with the use of such DLC overcoats. For example, the high coercivity media materials needed for perpendicular recording are very granular and rough. The currently available DLC overcoats, deposited by ion beam deposition are too directional and tend to preferentially deposit on the peaks of the rough granular surface of the media. In order to ensure complete coverage, the DLC coating must be deposited at least 4 or 5 nm thick. To make matters worse, future perpendicular media, with well segregated grains will be even harder to cover. The deposited DLC, when deposited on such materials does not spread well, making it very difficult to achieve a uniformly coated surface.
What is needed is a material that can provide adequate corrosion and mechanical protection at a thickness less than 3 nm. Such a material would preferably be easily applied, being capable of spreading evenly to uniformly coat a surface of the media. Such a material would also preferably incur little or no additional expense or manufacturing complexity.